Method for reducing spinneret deposits



May 26, 1959 FIG. PARKER METHOD FOR PRODUCING SPINNERET DEPOSITS Filed May 8, 1957 Big-2 INVENTOR FRANKLIN G. PARKER ATTORNEY United States PatentO METHOD FOR REDUCING SPINNERET DEPOSITS Franklin G. Parker, Wilmington, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application May 8, 1951, Serial No. 657,861

1 Claim. c1. 1s-.-s4

invention relates to the manufacture of regenerated cellulose yarns by the viscose process. More particularly, it is concerned with a method for reducing spinneret deposits, commonly known as'craters.

-In the viscose process for manufacturing regenerated cellulose yarns, the viscose solution containing cellulose xanthate is extruded through minute openings into a trough containing coagulating or precipitating medium. This medium is usually an aqueous acid bath containing sulfuric acid and soluble metal sulfates. 'Other in-' organic salts and various organic compounds such as reducing sugars may also be present. The xanthate is coagulated, regenerated as cellulose, and collected as rayon'yarn.

A problem at extrusion has resulted from so-called cratering caused by deposits in the form of craters on the spinneret around the extrusion orifices of material from the viscose solution or thespinning bath. These deposits tend to block the small extrusion orifices. Partial obstruction varies the thickness of individual filaments and" causes non-uniformity in the final product; Complete obstruction causes filament breaks. If a sufiicient number of orifices become clogged, spinning will be interrupted entirely. k I 1 The use of high temperature spinning baths, the presence in the baths of large quantities of zinc salts and the use of certain viscose or regenerating bath additives including the modifiers described in US. 2,535,044 US. 2,535,045, and US. 2,536,014 tend to intensify cratering. The presence of high zinc salt concentration renders the problem particularly acute.

"It has now been found that when viscose is extmded through a metal spinneret into an acid spinning bath, the spinneret develops a negativeelectrical potential. Hard deposits (craters) tend to build up rapidly'on the face of the spinneret when the spinneret develops an appreciable negative potential in this manner. This is thought to be due to the attraction of the negatively charged spinneret for the positive metal cations in the spinning bath. Y e

This problem has been aggravated by the increasing use of plastic parts such as spinneret caps, goosenecks, gasketing materials, candle filter housings and the like. Plastic. parts of this type are desirablebecause of their resistance to, corrosion but they serve to electrically insulate the spinneret so that an increasing electrical potential is built up on the spinneret and the cratering-eifect is substantially increased. 7

One object of this invention, th refore, is to inhibit spinneret cratering.

Another object is to provide an improved apparatus for viscose spinning which resists cratering.

These and other objects will become apparent in the course of the following specification and claim.

The above objects are accomplished by the present invention which provides a process and apparatus in which the electrical charge on the electrically insulated spinneret, which develops when the viscose is extruded 2,888,318 Patented May 26, 1959 "ice , 2 through such a spinneret into an acid sulfate coagulating and regenerating bath, is continuously removed by grounding the electrically insulated spinneret whereby the electrical 'potential on the spinneret is substantially reduced.

The present invention thus provides a non-cratering spinning assembly for the production of a regenerated cellulose filament which comprises an aqueous acid coagulating bath container, an electrically insulated metal spinneret contained therein and connected to a viscose supplyconduit, and a grounded electrical conductor attached to the said spinneret. By the term electrically insulated. is meant that the spinneret is not grounded or is not, grounded sufficiently to dissipate the electrical charge which builds up on the metal spinneret during extrusion. The term contained therein is used to signify that the spinneret is located within the confines of the bath container. In normal operation the liquid level of the aqueous acid coagulating bath is located somewhat above the spinneret.

Grounding may be conveniently accomplished by connecting the spinneret directly to the bath container, which is-metal and grounded, by means of an electrical conductor such as a platinum wire. Alternately, the spinneret may be connected by means of a metal conductor to any convenient piece of grounded metal equipment or it may be grounded directly in any other suitable manner.

The illustrations, although not essential to an understanding of the invention, show a preferred embodiment.

Figure 1 illustrates a system for the production of regenerated cellulose in accordance with the present invention.

Figure. 2 is an elevation partially in section showing the nature of a conventional spinneret coupling of a spinneret cap to its lead gooseneck.

Referring more particularly to Figure l, a viscose supply 1 is pumped through a candle filter 2 (the housing of which is often made of plastic) into a gooseneck 3 and spinneret 7 which is attached to gooseneck 3 by means of spinneret cap 6. The extruded viscose enters an aqueous acid bath 8 in lead trough 9 and is lead from the bath and collected by conventional collecting means, A metallic wire 5 connected directly to spinneret 7 grounds the spinneret 7 through the lead trough 9 by means of a ground connection 4 on the lead bath trough. The ground connection 4 may be the frame of the apparatus itself or a grounded metallic wire connectedto lead trough 9.

Figure 2 is an elevation partially in section showing Percent area reduction 1 X Where A ,=cratered area of spinneret orifices. Where A =total orifice area of clear spinneret.

The areas are measured by means of a camera lucida. This device is attached to a microscope and consists of a prism and a mirror arrangement which projects the microscopic image of the orifices on tracing paper adjacent to the microscope. The areas of the clean and cratered traces are measured by direct planimeter readings. The first example is a control run for comparison purposes.

aeeasre 3 EXAMPLE 1 A viscose spinning solution, containing 7% by weight of recoverable cellulose and 6% alkali calculated as sodium hydroxide, is extruded through a gold-platinum spinneret having 60 orifices (each of .003 inch diameter) into the spinning bath in a lead trough. 'I he bath contains 9% sulfuric acid, 14% sodium sulfate, and 12% zinc sulfate. It is maintained at a temperature of 50 C.

The yarn formed is stretched in the presence of hot dilute acid and collected on a bobbin. After a preliminary Wash the bobbin cake is up-twisted to form a flat wrap cake. Acid, soluble salts and sulfur compounds are then washed out with aqueous solutions of sodium bicarbonate, sodium carbonate, sodium cyanide, and sodium silicate. A final washing is with soft water. After suitable lubrication the yarn is dried and wound onto a paper core in the form of a cone. Samples of yarn are tested on the inclined plane tester, a Scott Machine Company product, for tenacity and elongation.

Due to poor performance spinning of the control is interrupted and the yarn tested after about two and onehalf hours of operation. The average reduction in orifice area is as reported in Table I. The electrical potential on the control spinnerets is measured with a Rulicon potentiometer and is found to range from 0.2 to 0.6 volt.

In each of Examples II to IV inclusive the spinneret is connected to the lead trough by means of a platinum wire (the trough being electrically grounded) thereby reducing the electrical potential to the range of zero to 0.05 volt. The spinning solutions employed are the same as those of Example I except for certain dispersing agent additives (at 0.05% concentration) made to the viscose as noted in Examples III and IV. Additives as employed and observations are listed in Table I. The properties of the yarns of Examples I and II are reported in Table II.

Table l Opera- Percent Example Additive tion Area Re- Perlod duction (hrs.)

2. 33 II 5 6 In {Ethylene diamine fatty acid 64 9 Alkylaryl polyoxthylene glycol IV ethoxylated rosin amine 3 112 3 1 Sold by the Nopco Chemical Co. of Harrison, N .J under the trade name N opco.

2 Sold by the Antara Chemicals 00., Division of General Dyestufi gogporation of Philadelphia, Pa, under the trademark Igcpal CA 3 Sold by Hercules Powder 00., of Wilmington, Delaware under the trademark Polyrad 2000. (Numeral prefix indicates moles of ethylene oxide per mole of rosin amine).

4 Table II Property ExalInple Exafiiple The nature of the metal employed in the construction of the spinneret is not critical. Spinnerets of gold, silver, platinum, palladium, tantalum and other alloys as commonly employed are all amenable to the present invention. The nature of the grounding conductor is not critical. Any material having low electrical resistance such as copper, silver, platinum and the like may be employed. In view of the acidic nature of the coagulating bath it is sometimes advantageous to coat the metallic conductor with relatively inert substances such as polythene to prevent attack by the regenerating bath. The electrical connection of the spinneret is generally made directly to the spinneret due to the insulating efiect of the gasketing materials, plastic parts, corroded or painted joints, etc. This insulation is usually suflicient to permit build-up of considerable static charge upon the spinneret.

While the reduction or elimination of the electrical potential on the spinneret is eifective in itself in the reduction of cratering, nevertheless, it is preferred to operate in the presence of anti-cratering additives, such as dispersing agents, either cationic, anionic or nonionic or mixtures thereof. Such materials are disclosed in United States Patents 2,125,031, 2,331,935, and 2,359,750. While the invention has been described with particularity in the spinning of regenerated cellulose from viscose, it is applicable generally to wet spinning processes where the spinning bath contains electrolytes. Thus the invention may be employed in the production of rayon by the cupramrnorn'um process.

This application is a continuation-in-part of application Serial No. 417,210, filed March 18, 1954.

Many equivalent modifications of the invention will be apparent to those skilled in the art from a reading of the above description without a departure from the inventive concept.

What is claimed is:

In a process for the formation of a regenerated cellulose filament by extruding viscose through an electrically insulated metal spinneret into an aqueous acid coagulating bath whereby an electrical charge is continuously built up on the spinneret during extrusion; the improvement which comprises continuously removing the said charge by means of a grounded electrical conductor attached to the said spinneret.

References Cited in the file of this patent UNITED STATES PATENTS 849,870 Waddell Apr. 9, 1907 1,389,517 Kitsee Aug. 30, 1921 1,590,592 Taylor et al. Tune 29, 1926 2,108,361 Asakawa Feb. 15, 1938 2,158,415 Formhals May 16, 1939 FOREIGN PATENTS 997,970 France Jan. 14, 1952 

1. IN A PROCESS FOR THE FORMATION OF A REGENERATED CELLULOSE FILAMENT BY EXTRUDING THROUGH AN ELECTICALLY INSULATED METAL SPINNERET INTO AN AQUEOUS ACID COAGULATING BATH WHEREBY AN ELECTRICAL CHARGE IS CONTINUOUSLY BUILT UP ON THE SPINNERET DURING EXTRUSION; THE IMPROVEMENT WHICH COMPRISES CONTINUOUSLY REMOVING THE SAID CHARGE BY MEANS OF A GROUNDED ELECTRICAL CONDUCTOR ATTACHED TO THE SPINNERET. 